Rotary compressor with capacity regulation valve

ABSTRACT

A rotary compressor being provided with a capacity regulation valve (16) at the outlet of the compressor. The valve is movable between a first position (18) in sealing cooperation with an end face (19) of the compressor rotor and a second position (20) creating a leakage path between the outlet opening (15) and the inlet opening (14) of the compressor.

The present invention relates to a rotary compressor particularly to arotary compressor provided with a simple and efficient valve forcapacity regulation of the compressor. The valve also allows unloadedstart of the compressor.

According to one prior art capacity regulation of a screw compressor theinlet channel is throttled so as to allow only a part of the fullcapacity gas flow to be delivered by the compressor. This is a simpleway of obtaining capacity regulation. However, the power required todrive the compressor at part load is rather close to the power requiredwhen the compressor runs at full capacity.

Another prior art solution provides for the returning of uncompressedgas to the inlet. This is accomplished by means of either a slide valvemovable in the wall of the compression chamber or a turn valve arrangedin the housing and communicating with the compression chamber. This ideaprovides for lower power requirement at a part load than the abovementioned prior art. However, the compressor becomes considerably morecomplicated.

According to a further prior art solution, U.S. Pat. No. 3,527,548,partly compressed gas is conducted back to the inlet through the rotorshaft. This solution results in a rather complicated rotor shaft whichfurthermore becomes less stiff so that rotor deflections increase. Thisresults in sealing problems.

The present invention, which is defined in the appended claims, aims atcreating a rotary compressor having a simple capacity regulation valvewhich provides for a part load power requirement which is substantiallylower than the power requirement of the throttled inlet capacityregulation.

An embodiment of the invention is described below with reference to theaccompanying drawings in which:

FIGS. 1a and 1b illustrate sections through one end of a screwcompressor in which FIG. 1a shows a valve in a sealing position, whileFIG. 1b is similar to FIG. 1a but shows the valve in an open position.

FIGS. 2 and 3 schematically show how the regulation valve operates.

FIG. 4 shows a view of the valve elements.

The rotary compressor shown in the drawings is a screw compressor andcomprises a housing 11 provided with two intersecting bores in which tworotors 12,13 are rotatable. Each rotor is provided with a number oflobes and intervening grooves. The rotors are provided with shafts 17which are journalled in bearings 25. The rotors convey compressiblefluid from an inlet opening 14 to an outlet opening 15 while compressingthe fluid. A valve element 16 is longitudinally slidable in housing 11along rotor shaft 17 which is provided with a sleeve 23 held in place bya nut 24. A valve element is provided for each rotor. A bushing 26containing a number of seals 27 is arranged in housing 11. Valve element16, provided with a seal 29, is movable between a first position 18,shown in FIG. 1a, in sealing cooperation with an end face 19 of rotor 13and a second position 20, shown in FIG. 1b, creating a leakage path,illustrated by arrows 21, between outlet opening 15 and inlet opening 14along the outer surface of the rotor. Valve element 16 is provided witha cut-out 22 so as not to unduly restrict the fluid flow at the outlet15. The valve is also slidable along a pin 30 inserted in ring 26 sothat valve 16 cannot turn in the housing 11. Valve element 16 is pushedtoward second position 20 by the gas pressure at the outlet end of thecompressor. In the illustrated embodiment of the invention valve element16 is pushed toward first position 18 by gas pressure applied throughchannel 28. It is also possible to use hydraulic pressure or mechanicalactuation of the valve element. The valve element can be positionedanywhere between the fully open position 20 and the closed position 18by controlling the pressure of the gas supplied through channel 28 viachamber 31.

I claim:
 1. A rotary compressor comprising a housing (11) provided withtwo intersecting bores, one rotor (12, 13) journalled for rotation ineach of said bores for conveying compressible fluid from an inletopening (14) to an outlet opening (15), each rotor comprising a numberof lobes and intervening grooves, characterized by a valve element (16)slideable in said housing (11) along at least one rotor shaft (17) of atleast one of said rotors between a first position (18) in sealingcooperation with an end face (19) of said at least one rotor and asecond position (20) creating a leakage path (21) between the outletopening (15) and the inlet opening (14) along the outer surface of saidat least one rotor, said valve element (16) comprising an annular ringguided by a pin (30) being immobile relative to the housing (11).
 2. Arotary compressor as claimed in claim 1, wherein said valve element (16)is partially disposed in said outlet opening and is provided with acut-out (22) to reduce flow losses at the outlet opening (15) of thecompressor.
 3. A rotary compressor comprising a housing (11) providedwith two intersecting bores, one rotor (12,13) journalled for rotationin each of said bores for conveying compressible fluid from an inletopening (14) to an outlet opening (15), each rotor comprising a numberof lobes and intervening grooves, characterized by a valve element (16)slidable in said housing (11) along a rotor shaft (17) of said rotorsbetween a first position (18) in sealing cooperation with an end face(19) of said rotors and a second position (20) creating a leakage path(21) between the outlet opening (15) and the inlet opening (14) alongthe outer surface of the rotors, said valve element (16) comprising anannular ring guided by a pin (30) being immobile relative to the housing(11).
 4. A rotary compressor comprising a housing (11) provided with twointersecting bores, one rotor (12,13) journalled for rotation in each ofsaid bores for conveying compressible fluid from an inlet opening (14)to an outlet opening (15), each rotor comprising a number of lobes andintervening grooves, characterized by a valve element (16) slidable insaid housing (11) along a rotor shaft (17) of said rotors between afirst position (18) in sealing cooperation with an end face (19) of saidrotors and a second position (20) creating a leakage path (21) betweenthe outlet opening (15) and the inlet opening (14) along the outersurface of the rotors, said valve element (16) comprising an annularring guided by a pin (30) being immobile relative to the housing (11),said valve element (16) being partially disposed in said outlet openingand being provided with a cut-out (22) to reduce flow losses at theoutlet opening (15) of the compressor.